The exemplary embodiment relates to increasing efficiency in an incandescent lamp. It finds particular application with regard to lamps comprising a tungsten or carbon filament, such as a rhenium and carbonitride containing filament, for reducing thermal stress and brittleness while increasing the efficiency of a lamp, and will be described with particular reference thereto.
Tungsten or carbon filaments for incandescent lamps are well known in the art. In most applications, the filaments are made of a wire which is wound into a coil. Coil dimensions determine not only the achievable light output of the lamp, but also the optical projector system of the lamp.
During filament production, the coiled filaments are annealed (heat treated to preserve the shape of the filament). This annealing serves to enable the assembly of the filaments on an automated mounting machine without breaking. During the annealing of the coils, that part of the coils made of tungsten wires tends to re-crystallize, at least partly, and mainly on the compressed side of the coil. This partial re-crystallization significantly increases the probability that the coil will break. This leads to the failure of the lamp in a short time. Since for these lamps, the allowed defect rate is critical for marketability, a high defect rate cannot be tolerated.
Thus, there remains a need for a lamp with improved thermal stress and reduced brittleness while providing desirable illumination and energy efficiency.